LTC3026EDDPBF

LTC3026 1.5A Low Input Voltage VLDO Linear Regulator FeaTures n DescripTion The LTC®3026 is a very low dropout (VLDO™) linear regulator that can operate at input voltages down to 1.14V. The device is capable of supplying 1.5A of output current with a typical dropout voltage of only 100mV. To allow operation at low input voltages the LTC3026 includes a boost converter that provides the necessary headroom for the internal LDO circuitry. Output current comes directly from the input supply to maximize efficiency. The boost converter requires only a small chip inductor and ceramic capacitor for operation. Additionally, the boosted output voltage of one LTC3026 can supply the boost voltage for other LTC3026s, thus requiring a single inductor for multiple LDOs. A user supplied boost voltage can be used eliminating the need for an inductor altogether. The LTC3026 regulator is stable with 10µF or greater ceramic output capacitors. The device has a low 0.4V reference voltage which is used to program the output voltage via two external resistors. The device also has internal current limit, overtemperature shutdown, and reverse output current protection. The LTC3026 is available in a small 10-lead MSOP or low profile (0.75mm) 10-lead 3mm × 3mm DFN package. n n n n n n n n n n n Input Voltage Range: 1.14V to 3.5V (with Boost Enabled) 1.14V to 5.5V (with External 5V Boost) Low Dropout Voltage: 100mV at IOUT = 1.5A Adjustable Output Range: 0.4V to 2.6V Output Current: Up to 1.5A Excellent Supply Rejection Even Near Dropout Shutdown Disconnects Load from VIN and VBST Low Operating Current: IIN = 950µA at VIN = 1.5V Low Shutdown Current: IIN < 1µA (Typ), IBST = 0.1µA (Typ) Stable with 10µF or Greater Ceramic Capacitors Short-Circuit, Reverse Current Protected Overtemperature Protected Available in 10-Lead MSOP and 10-Lead (3mm × 3mm) DFN Packages applicaTions n n n High Efficiency Linear Regulator Post Regulator for Switching Supplies Microprocessor Supply L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks and ThinSOT, VLDO are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Typical applicaTion 1.2V Output Voltage from 1.5V Input Supply 150 L1 10µH SW 5V BOOST BST CONVERTER IN 4.7µF 0.4V Dropout Voltage vs Output Current 4.7µF DROPOUT (mV) 100 VIN = 1.5V + – 1.2V 1.5V 2.0V 2.6V OUT 8.06k VOUT = 1.2V, 1.5A COUT 10µF 50 OFF ON SHDN LTC3026 GND ADJ 100k PG 4.02k 3026 TA01a 0 0 0.5 IOUT (A) 1.0 1.5 3026 TA01b L1: MURATA LQH2MCN100K02 3026fd  LTC3026 absoluTe MaxiMuM raTings (Note 1) VBST to GND ................................................. –0.3V to 6V VIN to GND ................................................... –0.3V to 6V PG to GND ................................................... –0.3V to 6V SHDN to GND............................................ –0.3V to 6.3V ADJ to GND................................... – 0.3V to (VIN + 0.3V) Output Short-Circuit Duration .......................... Indefinite Operating Junction Temperature Range (Note 8) ............................................. –40°C to 125°C Storage Temperature Range................... –65°C to 125°C Lead Temperature (MSE, Soldering, 10 sec) ......... 300°C pin conFiguraTion TOP VIEW IN IN GND SW BST 1 2 3 4 5 11 GND 10 OUT 9 OUT 8 ADJ 7 PG 6 SHDN TOP VIEW IN IN GND SW BST 1 2 3 4 5 11 GND 10 9 8 7 6 OUT OUT ADJ PG SHDN DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 40°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB MSE PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 40°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB orDer inForMaTion LEAD FREE FINISH LTC3026EDD#PBF LTC3026EMSE#PBF LEAD BASED FINISH LTC3026EDD LTC3026EMSE TAPE AND REEL LTC3026EDD#TRPBF LTC3026EMSE#TRPBF TAPE AND REEL LTC3026EDD#TR LTC3026EMSE#TR PART MARKING LBHW LTBJB PART MARKING LBHW LTBJB PACKAGE DESCRIPTION 10-Lead (3mm × 3mm) Plastic DFN 10-Lead Plastic MSOP PACKAGE DESCRIPTION 10-Lead (3mm × 3mm) Plastic DFN 10-Lead Plastic MSOP TEMPERATURE RANGE –40°C to 125°C –40°C to 125°C TEMPERATURE RANGE –40°C to 125°C –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 3026fd  LTC3026 elecTrical characTerisTics SYMBOL VIN IIN PARAMETER Operating Voltage Operating Current (BOOST ENABLED, LSW = 10µH) The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TJ = 25°C. VIN = 1.5V, VOUT = 1.2V, CIN = CBST = 4.7µF COUT = 10µF (all capacitors ceramic) unless otherwise noted. , CONDITIONS (Note 2) IOUT = 0mA, VOUT = 0.8V, VSHDN = VIN, VIN = 1.2V IOUT = 0mA, VOUT = 1.2V, VSHDN = VIN, VIN = 1.5V IOUT = 0mA, VOUT = 1.2V, VSHDN = VIN, VIN = 2.5V IOUT = 0mA, VOUT = 1.2V, VSHDN = VIN, VIN = 3.5V VSHDN = 0V, VIN = 3.5V l l MIN 1.14 TYP 1160 950 640 400 0.6 MAX 3.5 UNITS V µA µA µA µA IINSHDN Shutdown Current Inductor Size Requirement Inductor Peak Current Requirement 20 40 5.2 4.4 µA µH mA V V mA mA 4.7 150 VSHDN = VIN l 10 5 4.2 7 10 VBST VBSTUVLO Boost Output Voltage Range Boost Undervoltage Lockout Boost Output Drive (Note 3) 4.8 4.0 VIN < 1.4V VIN ≥ 1.4V (BOOST DISABLED, VSW = 0V or Floating) The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TJ = 25°C. VIN = 1.5V, VOUT = 1.2V, VBST = 5V, CIN = CBST = 1µF COUT = 10µF (all capacitors ceramic) unless otherwise noted. , SYMBOL VIN IIN IINSHDN VBST VBSTUVLO IBST IBSTSHDN PARAMETER Operating Voltage Operating Current Shutdown Current Boost Operating Voltage (Note 7) Undervoltage Lockout Boost Operating Current Boost Shutdown Current IOUT = 100µA, VSHDN = VIN VSHDN = 0V CONDITIONS (Note 2) IOUT = 100µA, VSHDN = VIN, 1.2V ≤ VIN ≤ 5V VSHDN = 0V, VIN = 3.5V VSHDN = VIN l l l l l l MIN 1.14 TYP 95 0.6 MAX 5.5 200 20 5.5 4.4 275 5 UNITS V µA µA V V µA µA 4.5 4.0 5 4.25 175 1 (BOOST ENABLED or DISABLED) The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TJ = 25°C. VIN = 1.5V, VOUT = 1.2V, CIN = CBST = 1µF COUT = 10µF (all capacitors ceramic) unless otherwise noted. , SYMBOL PARAMETER VADJ OUT IADJ IOUT ILIM en Regulation Voltage (Note 5) Programming Range Dropout Voltage (Note 6) ADJ Input Current Continuous Output Current Output Current Current Limit Output Voltage Noise f = 10Hz to 100kHz, IL = 800mA Boost Disabled Boost Enabled VIN = 1.5V, VADJ = 0.38, IOUT = 1.5A VADJ = 0.4V VSHDN = VIN CONDITIONS 1mA ≤ IOUT ≤ 1.5A, 1.14V ≤ VIN ≤ 3.5V, VBST = 5V, VOUT = 0.8V 1mA ≤ IOUT ≤ 1.5A, 1.14V ≤ VIN ≤ 3.5V, VBST = 5V, VOUT = 0.8V l l l l l MIN 0.397 0.395 0.4 TYP 0.4 0.4 100 MAX 0.403 0.405 2.6 250 100 UNITS V V V mV nA A A µVRMS µVRMS –100 1.5 3 110 210 3026fd  LTC3026 elecTrical characTerisTics SYMBOL PARAMETER VIHSHDN VILSHDN IIHSHDN IILSHDN VOLPG IOHPG PG SHDN Input High Voltage SHDN Input Low Voltage SHDN Input High Current SHDN Input Low Current PG Output Low Voltage Output Threshold (Note 4) CONDITIONS 1.14V ≤ VIN ≤ 3.5V 3.5V ≤ VIN ≤ 5.5V 1.14V ≤ VIN ≤ 5.5V SHDN = VIN SHDN = 0V IPG = 2mA PG High to Low PG Low to High l l l l (BOOST ENABLED or DISABLED) The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25°C. VIN = 1.5V, VOUT = 1.2V, CIN = CBST = 1µF COUT = 10µF (all capacitors ceramic) unless otherwise noted. , MIN 1.0 1.2 0.4 –1 –1 0.1 0.01 –12 –10 –9 –7 1 1 0.4 1 –6 –4 TYP MAX UNITS V V V µA µA V µA % % PG Output High Leakage Current VPG = 5.5V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. This IC has overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperatures will exceed 125°C when overtemperature is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 2: Minimum Operating Voltage required for regulation is: VIN ≥ VOUT(MIN) + VDROPOUT Note 3: When using BST to drive loads other than LTC3026s, the load must be high impedance during start-up (i.e. prior to PG going high). Note 4: PG threshold expressed as a percentage difference from the “VADJ Regulation Voltage” as given in the table. Note 5: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current range must be limited. When operating at maximum output current, the input voltage range must be limited. Note 6: Dropout voltage is minimum input to output voltage differential needed to maintain regulation at a specified output current. In dropout, the output voltage will be equal to VIN – VDROPOUT. Note 7: To maintain correct regulation VOUT ≤ VBST – 2.4V Note 8: The LTC3026E is guaranteed to meet performance specifications from 0°C to 125°C. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3026I is guaranteed over the full –40°C to 125°C operating junction temperature range. Note that the maximum ambient temperature is determined by specific operating conditions in conjunction with board layout, the rated package thermal resistance and other environmental factors. Typical perForMance characTerisTics IN Supply Current with Boost Converter Enabled 1.50 1.25 INPUT CURRENT (mA) 150 1.00 IBST (µA) 0.75 0.50 0.25 0 –40°C 25°C 85°C 1.0 1.5 2.0 2.5 VIN (V) 3.0 3.5 3026 G01 BST Supply Current with Boost Converter Disabled 200 200 IN Supply Current with Boost Converter Disabled 150 IIN (µA) 100 VBST = 5V –40°C 25°C 85°C 125°C 100 VBST = 5V –40°C 25°C 85°C 125°C 50 50 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 3026 G02 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 3026 G03 3026fd  LTC3026 Typical perForMance characTerisTics ADJ Voltage vs Temperature 404 403 ADJUST VOLTAGE (mV) INPUT CURRENT (µA) 402 401 400 399 398 397 396 –50 –25 0 25 50 VBST = 5V VIN = 1.5V VOUT =1.2V 75 TEMPERATURE (°C) 100 125 3026 G04 IN Shutdown Current 5.0 4.5 4.0 BST VOLTAGE (V) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 –50 2.5V –25 0 25 50 75 TEMPERATURE (°C) 1.2V 100 125 3026 G05 BST Voltage vs Temperature 5.050 VIN = 1.5V 5.025 1mA 1.5A 5.000 3.5V 4.975 4.950 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3026 G06 Dropout Voltage vs Input Voltage 200 180 160 RIPPLE REJECTION (dB) DROPOUT (mV) 140 120 100 80 60 40 20 0 1.2 1.4 1.6 1.8 2.0 2.2 –40°C 25°C 85°C 125°C 2.4 2.6 3026 G07 Ripple Rejection 60 10kHz 50 40 30 20 10 0 1.2 VBST = 5V VOUT =1.2V IOUT = 800mA COUT = 10µF 1.4 1.6 1.8 2.0 VIN (V) 2.2 2.4 2.6 3026 G08 Ripple Rejection 70 60 RIPPLE REJECTION (dB) 50 40 30 20 10 0 100 1000 VBST = 5V VIN = 1.5V VOUT =1.2V IOUT = 800mA COUT = 10µF 10000 100000 1000000 1E+07 FREQUENCY (Hz) 3026 G09 VFB = 0.38V IOUT =1.5A 1MHz 100kHz VIN (V) Shutdown Threshold 1200 RISE RISE FALL FALL RISE FALL 600 –40°C 25°C 125°C 1 2 3 VIN (V) 4 5 6 3026 G10 Output Current Limit 5.0 4.5 4.0 3.5 IOUT (A) 3.0 2.5 2.0 1.5 1.0 1.0 1.5 2.0 CURRENT LIMIT THERMAL LIMIT VBST – VOUT (V) VOUT = 0V TA = 25°C 2.22 2.20 2.18 2.16 2.14 2.12 2.10 2.08 2.06 2.04 2.5 VIN (V) 3.0 3.5 3026 G11 BST to OUT Headroom Voltage VSHDN THRESHOLD (mV) 900 300 2.02 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 3026 G12 3026fd  LTC3026 Typical perForMance characTerisTics Delay from Enable to PG with Boost Disabled 400 375 350 DELAY (µs) 325 300 275 250 VOUT = 0.8V ROUT = 8 –40°C 25°C 85°C 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 3026 G13 Delay from Enable to PG with Boost Enabled 5.0 4.5 4.0 3.5 DELAY (ms) 3.0 2.5 2.0 1.5 1.0 0.5 0 1.0 1.5 2.5 2.0 VIN (V) 3.0 3.5 3026 G14 Output Load Transient Response 1.5A IOUT 2mA VOUT = 0.8V ROUT = 8 –40°C 25°C 85°C OUT AC 20mV/DIV VOUT = 1.5V COUT = 10µF VIN = 1.7V VBST = 5V 50µs/DIV 3026 G15 IN Supply Transient Response SHDN 2V VIN 1.5V BST 1V 1.5V OUT 0V HI LO 5V BST/OUT Start-Up BST Ripple and Feedthrough to OUT VBST AC 20mV/DIV VOUT AC 10mV/DIV VOUT AC 5mV/DIV VOUT = 1.2V IOUT = 800mA COUT = 10µF VBST = 5V TA = 25°C 10µs/DIV 3026 G16 TA = 25°C ROUT = 1 VIN = 1.7V 200µs/DIV 3026 G17 VOUT = 1.2V VIN = 1.5V IOUT = 1A COUT = 10µF LSW = 10µH TA = 25°C 20µs/DIV 3026 G18 3026fd  LTC3026 pin FuncTions IN (Pins 1, 2): Input Supply Voltage. Output load current is supplied directly from IN. The IN pin should be locally bypassed to ground if the LTC3026 is more than a few inches away from another source of bulk capacitance. In general, the output impedance of a battery rises with frequency, so it is usually advisable to include an input bypass capacitor when supplying IN from a battery. A capacitor in the range of 0.1µF to 4.7µF is usually sufficient. GND (Pin 3, Exposed Pad Pin 11): Ground and Heat Sink. Connect the exposed pad to the PCB ground plane or large pad for optimum thermal performance. SW (Pin 4): Boost Switching Pin. This is the boost converter switching pin. A 4.7µH to 40µH inductor able to handle a peak current of 150mA is connected from this pin to VIN. The boost converter can be disabled by floating this pin or shorting this pin to GND. This allows the use of an external boosted supply from a second LTC3026 or other source. See Operating with Boost Converter Disabled section for more information. BST (Pin 5): Boost Output Voltage Pin. With boost converter enabled bypass the BST pin with a ≥4.7µF low ESR ceramic capacitor to GND (CBST). BST does not load VIN when in shutdown, but is diode connected to IN through the external inductor, thus, will not go to ground with VIN present. Users should not present any loads to the BST pin (with boost enabled) until PG signals that regulation has been achieved. When providing an external BST voltage (i.e. boost converter disabled) a 1µF low ESR ceramic capacitor can be used. SHDN (Pin 6): Shutdown Input Pin, Active Low. This pin is used to put the LTC3026 into shutdown. The SHDN pin current is typically less than 10nA. The SHDN pin cannot be left floating and must be tied to a valid logic level (such as IN) if not used. PG (Pin 7): Power Good Pin. When PG is high impedance OUT is in regulation, and low impedance when OUT is in shutdown or out of regulation. ADJ (Pin 8): Output Adjust Pin. This is the input to the error amplifier. It has a typical bias current of 0.1nA flowing into the pin. The ADJ pin reference voltage is 0.4V referenced to ground. The output voltage range is 0.4V to 2.6V and is typically set by connecting ADJ to a resistor divider from OUT to GND. See Figure 2. OUT (Pins 9, 10): Regulated Output Voltage. The OUT pins supply power to the load. A minimum output capacitance of 5µF is required to ensure stability. Larger output capacitors may be required for applications with large transient loads to limit peak voltage transients. See the Applications Information section for more information on output capacitance. 3026fd  LTC3026 block DiagraM SW 4 BOOST CONVERTER 5 BST SHDN 6 SWITCHING LOGIC EN SHDN 0.4V REFERENCE UVLO VOFF + – – 0.372V  – PG 7 +– + OVERSHOOT DETECT – + IN 1,2 OUT 9,10 8 ADJ GND 3,11 3026 BD + 3026fd LTC3026 operaTion The LTC3026 is a VLDO (very low dropout) linear regulator which operates from input voltages as low as 1.14V. The LDO uses an internal NMOS transistor as the pass device in a source-follower configuration. The BST pin provides the higher supply necessary for the LDO circuitry while the output current comes directly from the IN input for high efficiency regulation. The BST pin can either be supplied off-chip by an external 5V source or it can be generated through the internal boost converter of the LTC3026. Boost Converter Operation For applications where an external 5V supply is not available, the LTC3026 contains an internal boost converter to produce the necessary 5V supply for the LDO. The boost converter utilizes Burst Mode® operation to achieve high efficiency for the relatively low current levels needed for the LDO circuitry. The boost converter requires only a small chip inductor between the IN and SW pins and a small 4.7µF capacitor at BST. The operation of the boost converter is described as follows. During the first half of the switching cycle, an internal NMOS switch between SW and GND turns on, ramping the inductor current. A peak comparator senses when the inductor current reaches 100mA, at which point the NMOS is turned off and an internal PMOS between SW and BST turns on, transferring the inductor current to the BST pin. The PMOS switch continues to deliver power to BST until the inductor current approaches zero, at which point the PMOS turns off and the NMOS turns back on, repeating the switching cycle. A burst comparator with hysteresis monitors the voltage on the BST pin. When BST is above the upper threshold of the comparator, no switching occurs. When BST falls below the comparator’s lower threshold, switching commences and the BST pin gets charged. The upper and lower thresholds of the burst comparator are set to maintain a 5V supply at BST with approximately 40mV to 50mV of ripple. Care must be taken not to short the BST pin to GND, since the body diode of the internal PMOS transistor connects the BST and SW pins. Shorting BST to GND with an inductor connected between IN and SW can ramp the inductor current to destructive levels, potentially destroying the inductor and/or the part. Operating with Boost Converter Disabled The LTC3026 has an option to disable the internal boost converter. With the boost converter disabled, the LTC3026 becomes a bootstrapped device and the BST pin must be driven by an external 5V supply, or driven by the BST pin of a second LTC3026 with the boost converter enabled. The recommended method for disabling the boost converter is to simply float the SW pin. With the SW pin floating no energy can be transferred to BST which effectively disables the boost converter. A second method for disabling the boost converter is to short SW to GND. Shorting SW to GND to disable the boost converter should only be used in cases where IN is in its specified operating range when the LTC3026 is enabled. Enabling the part before VIN is in its operating range can cause current to be pulled off BST with the SW pin grounded. This can cause current limited supplies to hang under the right conditions. Connecting SHDN to IN will enable the part before IN is in its specified operating range. With SHDN connected to IN the SW pin should be floated to disable the boost converter. Either method of disabling the boost converter may be used if the signal driving the SHDN pin is high only when IN is in its specified operating range. Connecting SHDN to the power good pin of the supply driving IN is one method that allows both disable methods to be used. A single LTC3026 boost converter can be used to drive multiple bootstrapped LTC3026s with the internal boost converters disabled. Thus a single inductor can be used to power two (or possibly more) functioning LTC3026s. In cases where all LTC3026s have the same input supply (IN) the internal boost converters of the bootstrapped LTC3026s can be disabled by shorting SW to GND or floating the SW pin. If the LTC3026s are not all connected to the same input supply then the internal boost converters of the bootstrapped LTC3026s are disabled by floating the SW pin. If there is ever a doubt about which method to use remember that it is always safe to float the SW pin to disable the boost converter. There is no noticeable difference in performance of the part regardless of which disable method is used. 3026fd  LTC3026 operaTion LDO Operation An undervoltage lockout comparator (UVLO) senses the BST pin voltage to ensure that the bias supply for the LDO is greater than 4.2V before enabling the LDO. If BST is below 4.2V, the UVLO shuts down the LDO, and OUT is pulled to GND through the external divider. The LDO provides a high accuracy output capable of supplying 1.5A of output current with a typical dropout voltage of only 100mV. A single ceramic capacitor as small as 10µF is all that is required for output bypassing. A low reference voltage allows the LTC3026 output to be programmed to much lower voltages than available in common LDOs (range of 0.4V to 2.6V). The devices also include current limit and thermal overload protection, and will survive an output short-circuit indefinitely. The fast transient response of the follower output stage overcomes the traditional trade-off between dropout voltage, quiescent current and load transient response inherent in most LDO regulator architectures, see Figure 1. 1.5A IOUT 0mA the LDO reference voltage from 0V to 0.4V over a period of approximately 200µs, see Figure 2. SHDN HI LO 1.5V OUT 0V 1.5V PG 0V TA = 25°C ROUT = 1 VIN = 1.7V VB = 5V 100µs/DIV 3026 F02 Figure 2. Soft-Start with Boost Disable Adjustable Output Voltage The output voltage is set by the ratio of two external resistors as shown in Figure 3. The device servos the output to maintain the ADJ pin voltage at 0.4V (referenced to ground). Thus, the current in R1 is equal to 0.4V/R1. For good transient response, stability and accuracy the current in R1 should be at least 80µA, thus, the value of R1 should be no greater than 5k. The current in R2 is the current in R1 plus the ADJ pin bias current. Since the ADJ pin bias current is typically 125°C) should be avoided as it can degrade the performance or shorten the life of the part. Reverse Input Current Protection The LTC3026 features reverse input current protection to limit current draw from any supplementary power source at the output. Figure 6 shows the reverse output current limit for constant input and output voltages cases. Note: Positive input current represents current flowing into the VIN pin of LTC3026. With VOUT held at or below the output regulation voltage and VIN varied, IN current flow will follow Figure 6’s curves. IIN reverse current ramps up to about 16µA as the VIN approaches VOUT. Reverse input current will spike up as VIN approaches within about 30mV of VOUT as the reverse current protection circuitry is disabled and normal operation resumes. As VIN transitions above VOUT the reverse current transitions into short-circuit current as long as VOUT is held below the regulation voltage. 30 20 IIN CURRENT (µA) 10 0 LSW –10 –20 –30 IN CURRENT LIMIT ABOVE 1.45V CIN 1 IN 2 IN 3 GND 4 SW 5 BST 0 0.3 0.9 0.6 1.2 INPUT VOLTAGE (V) 1.5 1.8 3026 F06 Layout Considerations Connection from BST and OUT pins to their respective ceramic bypass capacitor should be kept as short as possible. The ground side of the bypass capacitors should be connected directly to the ground plane for best results or through short traces back to the GND pin of the part. Long traces will increase the effective series ESR and inductance of the capacitor which can degrade performance. With the boost converter enabled, the SW pin will be switching between ground and 5V whenever the BST pin needs to be recharged. The transition edge rates of the SW pin can be quite fast (~10ns). Thus care must be taken to make sure the SW node does not couple capacitively to other nodes (especially the ADJ pin). Additionally, stray capacitance to this node reduces the efficiency and amount of current available from the boost converter. For these reasons it is recommended that the SW pin be connected to the switching inductor with as short a trace as possible. If the user has any sensitive nodes near the SW node, a ground shield may be placed between the two nodes to reduce coupling. Because the ADJ pin is relatively high impedance (depending on the resistor divider used), stray capacitance at this pin should be minimized (